Overhead truck door opening and closing mechanism

ABSTRACT

An opening and closing mechanism for a roll-up cargo door for a truck is intended to decrease injuries to the people who load and unload items from box trucks and semi-trailers. The mechanism allows the user to open and close the overhead roll-up door of these trucks while standing firmly and safely on the ground at the rear corner of the truck. The door opening and closing mechanism is in the form of a loop of material that is attached to a lower portion of the roll-up door and a guide disposed near the top of the door frame. The loop is disposed along one of the vertical frame members of the door so that it is out of the way of the cargo hold when the door is open.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application claiming priority to U.S.patent application Ser. No. 15/695,806 filed Sep. 5, 2017, which issuedas U.S. Pat. No. 10,280,672 May 7, 2019, which claims the benefit ofU.S.

Provisional Patent Application Ser. No. 62/384,020 filed Sep. 6, 2016,and which is also a continuation-in-part of U.S. Pat. No. 10,076,951dated Sep. 18, 2018, which claims the benefit of U.S. Provisional PatentApplication No. 62/109,092 filed Jan. 29, 2015. The disclosures of eachdocument is incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE 1. Technical Field

The present disclosure generally relates to opening and closingmechanisms for overhead doors such as those used with box truck cargoholds or enclosed semi-trailers. More particularly, the presentdisclosure relates to opening and closing mechanisms for overhead doorsthat allow the user to open and close the overhead door while standingon the ground instead of climbing up on the truck.

2. Background Information

Cargo trucks that have overhead pull down doors are typically opened bythe user of the truck when the user unlatches the door from the truckbed and initially pushes it upwardly while the user is standing on theground. The doors are typically taller than a user's reach and the doorstypically do not glide all the way up to their fully open position. Whenthis occurs, the user must climb up onto the rear bumper of the truck orup into the cargo space to push the door to its fully open position.When the door is to be closed, the user almost always has to climb ontothe rear bumper of the truck or into the cargo area in order to reachthe door to pull it down to its closed position. Although some doorshave short hanging straps for the purpose of pulling them closed, mostpeople have to climb onto the truck bumper to reach the strap. Theprocess of climbing onto the bumper and jumping down from the bumperleads to injuries. The process of pulling down a door while the userstands on the bumper also leads to injuries. This is particularly riskyduring inclement weather especially when the bumper is wet,snow-covered, or icy. Delivery personnel who open and close truck doorsmultiple times per day desire a more convenient and safe or mechanismfor opening and closing the truck door.

SUMMARY OF THE DISCLOSURE

The mechanism configurations described in the following detaileddescription are intended to decrease injuries to the people who load andunload items from box trucks and semi-trailers. The mechanism allows theuser to open and close an overhead roll-up door of these trucks whilestanding firmly and safely on the ground at the rear corner of thetruck.

The disclosure provides a door opening and closing mechanism in the formof a loop of material that is attached to a lower portion of the roll-updoor and a guide disposed near the top of the door frame. The loop isdisposed on the outside of the door. A user can pull on one portion ofthe loop to open the door and on another portion of the loop to closethe door. The user can reach both of these portions while standingfirmly and safely on the ground. The disclosure also provides a roll-upoverhead door in combination with the opening and closing mechanism.

The disclosure provides a configuration wherein the loop is disposed outof the door opening so there is no potential interference of the loopwith the people and/or loaders moving into and out of the door opening.In one configuration, the loop is disposed along one of the verticalframe members that define the door opening.

The disclosure provides configurations wherein the loop includes anindicator that shows the user which side of the loop is to be pulleddown depending on the position of the door.

The disclosure provides configurations for the loop with differentgrips.

The disclosure provides different guide configurations carried bymounting brackets that can be secured to truck frames to allow theopening and closing mechanism to be retrofit onto existing truck frames.

The disclosure provides a motorized door opening and closing apparatuswherein an electric motor is used to selectively open and close thedoor. The apparatus includes a flexible loop attached to a lower portionof the door. An upper portion of the loop is driven by the motor to openand close the door. A toothed belt can be used to define the flexibleloop.

The mechanism described in this disclosure also can be used on anelevated overhead door on a building where in the user must climb uponto a structure to open and close it. Such a location can be anelevated loading dock.

The preceding non-limiting aspects, as well as others, are moreparticularly described below. A more complete understanding of theprocesses and equipment can be obtained by reference to the accompanyingdrawings, which are not intended to indicate relative size anddimensions of the assemblies or components thereof. In those drawingsand the description below, like numeric designations refer to componentsof like function. Specific terms used in that description are intendedto refer only to the particular structure of the embodiments selectedfor illustration in the drawings, and are not intended to define orlimit the scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a rear view of a truck with an overhead door partiallyopen with a first exemplary configuration of the opening and closingmechanism of this disclosure being depicted on the left-hand side of thedoor.

FIG. 2 is an enlarged perspective view of the upper left hand corner ofthe door frame showing an exemplary configuration for the guide usedwith the opening and closing mechanism.

FIG. 3 is a perspective view of the lower left hand corner of the doorframe with the door in a closed configuration with a portion of the loopbroken away to show the connection of the loop with the door.

FIG. 4 is a section view taken through the door showing a side view ofthe connection between the loop and the door.

FIG. 5 is an enlarged perspective view of the upper left hand corner ofthe door frame showing another exemplary configuration for the guideused with the opening and closing mechanism.

FIG. 6 is an enlarged perspective view of the upper left hand corner ofthe door frame showing another exemplary configuration for the guideused with the opening and closing mechanism.

FIG. 7 is a perspective view of an exemplary guide and mounting bracketfor the mechanism that allows the mechanism to be retrofit onto existingtruck frames.

FIG. 8 is a perspective view of an exemplary guide and mounting bracketfor the mechanism that allows the mechanism to be retrofit onto existingtruck frames.

FIG. 9 is a side view of the overhead door and mechanism of FIG. 1 inthe closed condition.

FIG. 10 is a side view of the overhead door and mechanism of FIG. 1 inthe open configuration.

FIG. 11 depicts a rear view of a truck with an overhead door in theclosed configuration with another exemplary configuration of the openingand closing mechanism of this disclosure being depicted on the left-handside of the drawing.

FIG. 12 is an enlarged view of the top of the mechanism depicted in FIG.11.

FIG. 13 is an enlarged view of the bottom of the mechanism depicted inFIG. 11.

FIG. 14 is a side view of the overhead door and mechanism of FIG. 11 inthe closed condition.

FIG. 15 is a side view of the overhead door and mechanism of FIG. 11 inthe open configuration.

FIG. 16 is a view similar to FIG. 14 showing a configuration wherein thelower pulley is disposed under the truck bed.

FIG. 17 is a side view of an alternative configuration for the loopmaterial.

FIG. 18 depicts an alternative view of an upper guide used with the loopmaterial of FIG. 17.

FIG. 19 depicts a spring-biased version of the FIG. 18 configuration.

FIG. 20 is a view similar to FIG. 2 depicting an alternative guide thathas a roller.

FIG. 21 is an elevation view of an alternative configuration wherein amotor is used to provide the opening and closing force to the apparatus.

FIG. 22 is an enlarged elevation view of the motor and drive for theloop.

FIG. 23 is a section view taken along line 23-23 of FIG. 22.

FIG. 24 is a view similar to FIG. 23 depicting an alternative motor anddrive for the loop.

FIG. 25 depicts a perspective view of an alternate mount for the loop.

FIG. 26 is a top view of the mount of FIG. 25.

FIG. 27 is an end view of the mount of FIG. 25.

FIG. 28 is a bottom view of the mount of FIG. 25 showing an alternativesleeve with the loop depicted schematically.

FIG. 29 is a rear elevation view of the mount of FIG. 25.

FIG. 30 is a front elevation view of the mount of FIG. 25.

FIG. 31 is an elevation view of a truck with an overhead door with anopening and closing mechanism disposed out of the door opening.

FIG. 32 is a side view of the truck door and vertical frame member withthe opening and closing member depicted without the sidewalls, floor, orroof of the cargo hold.

FIG. 33 is a section view taken along line 33-33 of FIG. 31.

FIG. 34 is an enlarged elevation view of the lower encircled portion ofFIG. 31.

FIG. 35 is an enlarged elevation view of the upper encircled portion ofFIG. 31.

FIG. 36 is an enlarged elevation view of the encircled portion of FIG.32.

Similar numbers refer to similar elements throughout the specification.

DETAILED DESCRIPTION OF THE DISCLOSURE

The different embodiments of the opening and closing mechanism of thisdisclosure is generally indicated by the reference number 10 in theaccompanying drawings. Opening and closing mechanism 10 allows anoverhead cargo door 18 of the truck 20 to be opened and closed while aperson is standing firmly on the ground at the back rear corner of truck20. Mechanism 10 generally includes a flexible loop 14 that is connectedto a lower portion 16 of door 18 and is supported from above by a guide12 that allows loop 14 to be moved between first and second positionsthrough guide 12. Loop 14 is disposed on the exterior of door 18.Mechanism 10 allows the user to open door 18 by pulling down one portionof loop 14 and then to close door 18 by pulling down on another portionof loop 14. Both the opening and the closing of door 18 are achieved bypulling down on portions of loop 14. Opening and closing mechanism 10may be built into new trucks or it can be retrofit to existing trucks20.

A first exemplary configuration of an opening and closing mechanism ofthis disclosure is generally shown on the left side of FIG. 1 and shownin more detail in FIGS. 2-6. Mechanism 10 generally includes an upperguide 12 and a flexible loop 14 that extends between guide 12 and alower portion 16 of the truck door 18. Loop 14 can be continuous orbroken by a connector, a buckle, or with a portion of loop 14 beingformed by a portion of door 18. The ends of loop 14 can be connected todoor 18 at the same location or different locations. Mechanism 10 isused with overhead roll-up truck doors that typically have a pluralityof hinged panels that ride on tracks disposed at the sides of thetrailer opening and project inwardly from the top of the opening. Loop14 is attached to the lowermost hinged panel with an anchor 28.

In the exemplary configuration of FIGS. 1-6, guide 12 is provided in theform of a thin bar having a rounded cross section. Loop 14 slidesdirectly over the rounded profile of guide 12. The thin bar that definesguide 12 can be mounted directly to the frame members of truck 20 or,alternatively, to a mounting bracket 42 that is used to connect guide 12to truck 20. In an alternative configuration of FIG. 20, the horizontalbar of guide 12 includes a roller 21 that freely rotates with respect tothe other portions of guide 12 so that loop 14 more easily moves betweenits first and second positions.

As shown in FIGS. 2, 5, 6, 7, 8, 12, 13, 18, 19, and 25 guide 12 can beprovided in the form of a pulley, a roller, a passive guide, a slide, oran eye-bolt. Each of these guides 12 can be secured to the truck 20 witha rigid connection or a biased connection such as depicted in FIG. 19.The biased connection includes a spring 22.

Mounting bracket 42 is provided with closed right angle inner corner asshown in FIG. 2. An alternative mounting bracket 42 is depicted in FIG.5 with an angled inner corner to accommodate an angled reinforcementplate 43 disposed at the corner of the truck frame. Another alternatemounting bracket 42 has an opening 45 that allows the angledreinforcement plate 43 to extend through mounting bracket 42. Mountingbracket 42 defines a plurality of openings 47 that allow mountingbracket 42 to be secured to truck 20 with fasteners such as metalscrews, bolts, or rivets. Mounting bracket 42 also can be welded totruck 20. FIG. 8 depicts a configuration of mounting bracket 42 with anintegral angled reinforcement plate 49 that strengthens the corner ofthe truck frame. In the FIG. 8 configuration, guide 12 is an openingdefined by the body of mounting bracket 42.

Mounting bracket 42 can include an L-shaped front face 51 that definesfastener openings 47. Mounting bracket 42 also includes sidewalls 53 towhich guide 12 is connected. Sidewalls 53 are generally perpendicular tofront face 51 and generally perpendicular to each other. Mountingbracket 42 can be added to the corner of an existing truck door framethat defines the door opening of a truck. Mounting bracket 42 thusprovides a convenient method to retrofit an existing truck door framewith mechanism 10. Once mounting bracket 42 is connected at the cornerof the door frame, guide 12 is positioned near the edge of door 18 andloop 14 can be positioned through guide 12 and secured to door 18.

FIG. 9 shows the closed position of door 18 and the first position ofloop 14. In this position, loop 14 is disposed between guide 12 and door18 and can be taut to minimize flapping in the wind while the truck ismoving. FIG. 10 depicts the open position of door 18 and the secondposition of loop 14. As shown in FIG. 10, the upper guide 12 ispositioned above the upper location of the lower end 26 of door 18 whendoor 18 is fully open. This allows loop 14 to be secured to the lowerportion 16 of door 18. When door 18 is raised to the open position, thelocation of the anchor 28 that secures loop 14 to door 18 stops justbelow upper guide 12. This configuration allows the remainder of loop 14to hang loosely.

One configuration of anchor 28 includes a pair of brackets 27 that eachdefine a slot to receive an end of loop 14 and a bolt hole. Brackets 27are bolted to door 18 with a single nut 29 and bolt 31 combination. Thenut can be disposed on the inside of door 18. As an alternative, anchor28 can be a clamp that secures a portion of loop 14 to door 18. In oneconfiguration, loop 14 can be fitted through one or more openingsdefined by door 18.

In the exemplary configuration of FIGS. 11-16, a lower guide 12 is usedat the bottom of the truck frame to hold the position of loop 14 whendoor 18 is open. The lower guide 12 can be in the form of any guide 12described above. In this configuration, guides 12 are in the form ofpulleys. In the FIG. 16 configuration, the lower guide 12 is positionedunder the floor. When the lower guide 12 is installed below floor 30, asingle opening 32 or a plurality of openings 32 are defined by floor 30to receive loop 14. In these configurations and the configurations ofFIGS. 21-24, a motor 80 can be used to move loop 4. Motor 80 can belocated near the upper guide, the lower guide, above the truck bed orbelow the truck bed. A housing can be used to protect motor 80 from theweather. Motor 80 can drive pinch rollers 82 that drives a flat straploop 14 or a toothed roller 84 that drives a toothed strap (seereference numeral 86 in FIG. 23) loop 14. This loop 14 can be made froma chain, a cable with knobs, or a toothed belt. A limit switch can beused to turn off the motor with a sensor carried by the loop or thedoor. As this sensor passes the limit switch, a signal is sent to themotor that turns the motor off. The motor can be controlled with manualswitches, automated switches, or a remote control that uses RF signals,Bluetooth, or other wireless communications protocols. Motor 80 can bepowered by its own power source or the power source carried by thetruck. In other configurations, motor 80 can be used without the lowerguide. In these configurations, a stiff or loop of stiff links is usedto push the door down by motor 80. In another configuration, motor 80rotates or gear or roller that directly engages the door to move it upand down.

FIG. 21 depicts an optional extension 88 connected to loop 14 that hangsdown to help a user pull the door closed at the end of the closingprocess. This can be useful when the user's hand is close to anchor 28.Instead of being pinched between the sides of loop 14, the user cangrasp extension 88 and finish the closing process. When not in use,extension 88 can be secured by a magnet 90 (either carried by extension88 or with a magnet carried by truck and a ferrous metal carried byextension 88) or a section of hook and loop material (such as Velcro®)that holds extension 88 to another portion of loop 14 or the truck.Extension 88 can be one foot or up to four feet long. Extension 88 canbe made from the same material as loop 14 or a material comfortable tograsp. Extension 88 can be used with the manual loop or the motorizedloop.

In the configuration of FIGS. 1-10, only the upper guide 12 is used withloop 14 hanging loose when door 18 is open. This configuration does notrequire the lower guide and does not present any risk of a tripping orunloading hazard in the lower corner of the door opening. When door 18is open, the loosely hanging loop14 can be pulled out of the way andsecured in a position that is out of the user's way until it is need toclose door 18.

Loop 14 can be formed from a strapping material. In one configuration,the strap material is one to three inches wide and one-sixteenth to ahalf inch thick. The strap material can be 1.500 inches wide and 0.125inches thick or 2.000 inches wide and 0.125 inches thick. Loop 14 can bea solid material such as a solid polymer or fiber strap or a wovenmaterial. A woven polymer such as woven polypropylene, woven polyester,or woven Nylon can be used. The strapping material can be folded anddoubled over itself when grasped by the user so that the user can obtaina good grip on loop 14 to pull down. In other configurations, loop 14 isformed from an endless or spliced belt, a cable, a chain, a rope, or awire. A stainless steel cable can be used.

In any of these configurations, the portion of loop 14 that is pulleddown to move door 18 is provided with an indicator to identify thatportion of loop 14 to the user. The indicator can be a color, a changein size of loop 14, a change in material, or a plurality of lugs 40formed or added to the portion of loop 14 that I to be pulled. In oneexample, loop 14 defines an outer portion and an inner portion when thedoor is closed as depicted in FIG. 9 with the outer portion beingdisposed to the left of the inner portion in the drawing. Each of theouter and inner portions has an outward-facing surface and a door-facingsurface. In this configuration, the user must grasp and pull down on theouter portion of loop to open door 18. As such, the outward-facingsurface of outer portion of loop can include an indicator that informsthe user that it is the correct portion of loop 14 to be pulled to opendoor 18. When the user opens the door as shown in FIG. 10, the surfaceof the outer portion that was door-facing has rotated around to be theouterward-facing surface of the inner portion. This surface can also beprovided with an indicator that tells the user that it is the portion ofloop 14 that is pulled down to close door 18. The indicators can bearrows, a different color, or a logo or trademark.

FIG. 17 depicts a configuration wherein a plurality of lugs 40 aredisposed along half or about 40 percent of the length of loop 14. Lugs40 can be actual lugs that are tied into the material of loop 14. Inother configurations, lugs 40 are items connected to loop 14. Forexample, the items that form lugs 40 can be malleable metal slugs thatare crimped onto or riveted into loop 14 or polymer slugs with lockingteeth that are snap fit onto loop 14. In other configurations, lugs 40can be secured to loop 14 with adhesive, welding, fusing, or friction.Lugs 40 are round or tapered on both ends to help them move throughguides 12. When lugs 40 are provided on only a portion of loop 14, theuser can use the lugs to identify which side of the loop to pull on toopen or close the door. For example, in FIG. 9, lugs 40 would be addedto the outer portion of loop 14 which is the half of loop 14 disposedfarthest away from door 18. In this configuration the user grasps thelugs and pulls down to open the door. As door 18 is opened, the lugs aremoved to the inner half of loop 14. In the configurations of mechanism10 using lugs 40, guide 12 can be configured to allow lugs 40 to slideover or around guides 12. For example, FIGS. 18 and 19 depict exemplaryguides 12 that are U-shaped in cross section and are sized to allow lugs40 to slide through guides. When pulleys are used as guides 12, eachpulley can use a U-shaped guide surface similar to FIGS. 18 and 19.Alternatively, a roller guide can define indents or notches thataccommodate the movement of the lugs through the roller guide.

Loop 14 and/or guides 12 can be enclosed within a housing that surroundsguides and/or loop 14. Lower guide 12 can be readily removable andreplaceable from truck 20 to allow a person unloading the truck to pullmechanism 10 out of the way if needed. A pinned connection between lowerguide 12 and truck 20 can be used for this quick connection.

FIGS. 25-30 depict mounting brackets 90 that support guide 12. Thesebrackets use one or two door hinge plates 92 and a U-bolt 94 to defineguide 12 over which loop 14 moves. Side plates 96 can be used to supportthe legs of U-bolt 94 and can be used to contain a rotating sleeve 21(shown for example in FIG. 28). Sleeve 21 can be nylon. One or bothplates 92 can be mounted to the underside of the door frame or to theouter surface of the door frame to mount guide 21.

In FIGS. 31-36, loop 14 and one or more guides 12 are disposed inalignment with one of the vertical members 23 of the door frame. Loop 14is disposed along the length of vertical frame member 23. As shown inFIG. 31, the majority of the length of loop 14 is disposed between theside edges of the vertical frame member 23. This configuration locatesloop 14 laterally outwardly of the door opening when the door is open sothat loop 14 does not interfere with workers or equipment entering orexiting the truck. Guide 12 can be disposed at the top of the truckframe or below the upper portion of the door where the lower edge of thedoor is located when the door is completely open. A single guide 12 canbe used at the top of the frame or a pair of guides 12 can be used atthe top and bottom of the frame. The pair of guides 12 prevents the loopfrom being loose when door 18 is open. These can be installed on eitherside of the door opening.

A bracket 25 is used to connect loop 14 to door 18. Bracket 25 can be arigid member configured to match the offset between the door 18 andframe 23 as shown in FIG. 33. An offset bracket 25 with a pair of rightangles can be used. This bracket 25 can be spaced from the door frame 23or can slide against a portion of the frame. Bracket 25 also can be madefrom a flexible material such as a short section of the material used toform loop 14. Bracket 25 can be connected to the inner portion of loop14 so that the user can pull down on the outer portion of the loop toopen the door. When the door is open, the user can down on the innerportion of the loop or pull up on the outer portion of the loop to closethe door.

In the foregoing description, certain terms have been used for brevity,clearness, and understanding. No unnecessary limitations are to beimplied therefrom beyond the requirement of the prior art because suchterms are used for descriptive purposes and are intended to be broadlyconstrued. Moreover, the description and illustration of the inventionis an example and the invention is not limited to the exact detailsshown or described. Modifications and alterations of those embodimentswill be apparent to one who reads and understands this generaldescription. The present disclosure should be construed as including allsuch modifications and alterations insofar as they come within the scopeof the appended claims or equivalents thereof. Throughout thedescription and claims of this specification the words “comprise” and“include” as well as variations of those words, such as “comprises,”“includes,” “comprising,” and “including” are not intended to excludeadditives, components, integers, or steps.

1. A cargo truck comprising: an enclosed cargo hold with a door framedefined by spaced first and second vertical frame members and an uppercross frame member that is joined to the first and second vertical framemembers to define two upper corners; the door frame defining a dooropening for the cargo hold; a door having a lower door portion; the doorbeing movable between open and closed positions with respect to thecargo hold of the truck; the closed position of the door closing thedoor opening; an opening and closing mechanism for opening and closingthe door; the opening and closing mechanism having first and secondguides; and a loop having portions passing over the first and secondguides in a manner that allows the loop to be moved with respect to theguides; the positions of the first and second guides being fixed withrespect to the door frame; the loop being disposed outside of the cargohold when the door is closed such that the loop is readily accessiblefor manipulation by a person opening the door; the loop being connectedto the lower door portion; and the loop being adapted to raise the doorfrom its closed position toward its open position and then lower thedoor from its open position towards its closed position when pulled downtoward the ground.
 2. The truck of claim 1, wherein the loop is disposedalong the first vertical frame member.
 3. The truck of claim 1, whereinthe loop is connected to the lower door portion with an anchor.
 4. Thetruck of claim 1, wherein the loop is defined by a flat strap.
 5. Thetruck of claim 4, wherein the flat strap is made from a woven polymer.6. The truck of claim 1, wherein at least one of the guides includes abar.
 7. The truck of claim 6, further comprising a roller carried by thebar.
 8. The truck of claim 1, wherein the loop is disposed vertically.9. The truck of claim 1, further comprising a floor; the door abuttingthe floor in the closed position of the door; the second guide beingdisposed under the floor.
 10. An improved opening and closing mechanismfor a cargo truck door on a cargo truck wherein the cargo truck has anenclosed cargo hold with a door frame defined by spaced first and secondvertical frame members and an upper cross frame member that is joined tothe first and second vertical frame members to define two upper corners;the door frame defining a door opening for the cargo hold; and a doorhaving a lower door portion; the door being movable between open andclosed positions with respect to the cargo hold of the truck; the closedposition of the door closing the door opening; the improvementcomprising: the opening and closing mechanism having first and secondguides; and a loop having portions passing over the first and secondguides in a manner that allows the loop to be moved with respect to theguides; the positions of the first and second guides being fixed withrespect to the door frame; the first guide being connected to the truckat a location above the lower portion of the door when the door is inthe open position; the loop being disposed outside of the cargo holdwhen the door is closed such that the loop is readily accessible formanipulation by a person opening the door; the loop being connected tothe lower door portion; and the loop being adapted to raise the doorfrom its closed position toward its open position and then lower thedoor from its open position towards its closed position when pulled downtoward the ground.
 11. The improvement of claim 10, wherein the loop isdisposed along the first vertical frame member.
 12. The improvement ofclaim 10, wherein the loop is connected to the lower door portion withan anchor.
 13. The improvement of claim 10, wherein the loop is definedby a flat strap.
 14. The improvement of claim 13, wherein the flat strapis made from a woven polymer.
 15. The improvement of claim 10, whereinat least one of the guides includes a bar.
 16. The improvement of claim15, further comprising a roller carried by the bar.
 17. The improvementof claim 10, wherein the loop is disposed vertically.
 18. Theimprovement of claim 10, wherein the cargo truck includes a floor; thedoor abutting the floor in the closed position of the door; the secondguide being disposed under the floor.